Valves are vital in water systems, controlling flow and access, preventing backflow, as well as managing pressure. Air valves specifically release trapped air to improve pumping efficiency and admit air to avoid vacuums, protecting pipelines from collapse while safeguarding the integrity of water and wastewater systems.

Dynamic Fluid Control (DFC), a leading valve manufacturer, is committed to developing innovative solutions that address real-world challenges. One such example was in America, where heavy fines for low pressure-related sewage leaks prompted the design of a new range of valves (RGXII).

Low pressure sealing valves

Jonathan Suter, research and development engineer at DFC, says, “Our latest innovation, the RGXII low-pressure sealing valve can seal effectively at very low pressures to prevent sewage leaks.” He explains that the RGXII is shorter, lighter and more buoyant with improved O ring seals than its predecessor and seals at pressures below 0.21 bar.

“The result is low-pressure sealing without sacrificing high-pressure performance. The design is patented in America, Canada, the United Kingdom, Australia, and South Africa. In fact, the low-pressure sealing works so well we are rolling it out on other models.”

The initial focus was on a DN50 version that could seal effectively at less than 21 kPa. Following its success, the design was expanded to include larger sizes: DN80, DN100, DN150 and DN200. The RGXII concept also allows retrofitting into existing RGX bodies that use the original polyurethane lower floats.

Advantages over older and competitor designs include:

• Sealing at pressures as low as 7 kPa
• Improved lower float buoyancy from trapped air and increased float volume, resulting in low pressure sealing
• Shorter overall height for confined chambers
• Proven durability in sewage and wastewater environments’.

“The lower height of the RGXII valve is particularly useful in underground closed valve chambers where chamber cover height restrictions are imposed. Its unique float cage allows for easy float extraction maintenance,” explains Suter.

Furthermore, the anti-surge float technology is a pressure spike alleviation mechanism that protects the pipeline in the event of sudden air valve closure. The anti-surge or anti shock float does not fully close or slam shut when a sudden rush of fluid and air comes through the pipeline. The air valve continues to vent air through the small orifice while creating an air cushioned accumulator or gas spring that decelerates the fast-approaching fluid over a longer distance. It also ensures that the fast-moving liquid does not come to a sudden stop.

Feedback from real-world application

In South Africa, Siza Water, a water utility in KwaZulu-Natal, received the RGXII as part of their operations and report that, “Before partnering with DFC, we encountered challenges related to air accumulation in pipelines–leading to inefficiencies, pressure fluctuations, and increased strain on critical infrastructure. Traditional air valves required frequent maintenance and were prone to premature failure, causing operational disruptions.

From installation there has been 60% less interventions in terms of maintenance in 3 months, and the valves’ 15-year lifespan puts Siza Water at ease.

Other valve applications

As the RGXII is designed for sewer applications, Isaac Mahlangu, technical analyst at DFC adds that for potable water applications, the company offers the RBX and RBXc (ast body) valves.

“The RBX comes in a variety of materials, including stainless steel grades 304 and 316, duplex, super duplex, and materials suitable for seawater or brine applications.”

Irrigation systems utilise RC and RPS valves, with the former featuring a cast iron body and the latter made from nylon 6 plastic, tailored for durability in diverse environments.

The problem with air

According to Mahlangu, air valves are vital because trapped air inside pipelines occupies space and this increases pumping time and energy costs. “Air is compressible, so you need to push harder to pump the water through your pipeline.” Left unmanaged, this can lead to airlocks that disrupt flow and efficiency.

Beyond operational inefficiencies, the presence of air in pipes can encourage the growth of organic materials in pipelines that sometimes leads to corrosion.

To counter these issues, air valves are strategically placed at the highest points along pipelines where air naturally accumulates because air bubbles and pockets always move to the highest points. This makes these locations ideal for valve installation to ensure timely release and vacuum breaking, thereby safeguarding the system.

With pumps, valve arrangements are carefully designed for optimal performance. For example, with turbine or centrifugal pump setups, a non-return valve prevents backflow while an air valve promptly releases entrapped air to reduce turbulence. “You need to release air immediately from the pump,” Mahlangu emphasises.

Sizing these valves correctly is critical. Unlike standard gate or butterfly valves that are sized based on pipe diameter, air valves must be sized based on their capacity to admit and release air. Using a 600 mm diameter pipeline with a flow of 424 litres per second as an example, DFC recommends an 80 mm valve size. The company provides detailed sizing charts available in their catalogues and online.

CATT Program

To assist engineers and designers, DFC has developed the Controlled Air Transfer Technology (CATT) software, a free, globally accessible program for precise valve sizing and placement. After registering, users input pipeline coordinates, fluid type, flow parameters, and pipe material into the software.

The program analyses the data and recommends optimal valve locations, considering critical factors such as the hydraulic gradient line, which affects valve function and prevents siphoning. Users can also manually input scour and isolation valves to tailor the system further.

“The software allows you to optimise your valve placement and produces detailed reports, including economic assessments and pipeline profiles,” the representative explains.

“Valves may look simple,” concludes Mahlangu, “but their design and placement are critical to keeping pipelines efficient, reliable, and protected from damage. That is why, beyond manufacturing and designing valves, DFC also provides technical support, valve repair, site audits, and training.”